Alkanediols, especially vicinal alkanediols, such as 1,2-alkanediols, 2,3-alkanediols, 3,4-alkanediols, and their higher homologs, are typically produced by hydrolysis of epoxyalkanes. For certain commercial applications the alkanediol must meet stringent low odor specifications.
A practical commercial method for producing the epoxyalkane starting materials involves reaction of an alkene with hydrogen peroxide in the presence of a heavy metal catalyst system, such as a tungsten-based catalyst. While effective, such processes can produce small amounts of coproducts as impurities. Unless removed trace amounts of such impurities tend to produce commercially unacceptable odors in the alkanediols produced therefrom. A case in point is 1,2-hexanediol, a commercially important product for which there is a stringent odor specification which must be satisfied.
While it is possible to purify epoxyalkanes by distillation, this necessitates in commercial practice use of an expensive distillation operation involving use of expensive distillation equipment. A need thus exists for a simpler and more economical way, compared to expensive distillation, of removing the odor components and/or their precursors so that the final alkanediol product has reduced odor characteristics, and enabling the product to meet odor specifications which maybe applicable to the product. It would be particularly desirable if a chemical treatment method could be found for fulfilling this need without adversely affecting the product or materially reducing the yield of the finished product.
This invention is deemed to fulfill the foregoing need in a highly effective manner.
This invention provides commercially attractive ways of preventing undesired odors in alkanediols, especially alkanediols produced from epoxyalkanes, and most especially in vicinal alkanediols such as 1,2-alkanediols formed from corresponding vicinal epoxyalkanes such as 1,2-epoxyalkanes. In addition, this invention makes it possible to provide commercially attractive ways of purifying epoxyalkanes including those intended for use as raw materials in the synthesis of alkanediols.
Among the various embodiments of this invention is a process of treating at least one epoxyalkane such that if the epoxyalkane is hydrolyzed to form at least one alkanediol, undesirable odor in the resultant alkanediol is reduced or eliminated. The process comprises subjecting the epoxyalkane(s) to at least one of the following washing operations:
(i) washing the epoxyalkane(s) at least once with an aqueous washing solution of inorganic base, and then washing the epoxyalkane(s) at least once with an aqueous washing solution of borohydride; or
(ii) washing the epoxyalkane(s) at least once with an aqueous washing solution of borohydride, and then washing the epoxyalkane(s) at least once with an aqueous washing solution of inorganic base; or
(iii) washing the epoxyalkane(s) at least once with an aqueous washing solution of both inorganic base and borohydride;
such that undesirable odor is reduced or eliminated from alkanediol(s), if produced from the treated epoxyalkane(s) by hydrolysis. In washing operations (i) and (ii) at least two aqueous washes are carried out, one of which is conducted using an aqueous solution of an inorganic base, and the other of which is conducted using an aqueous solution of a water-soluble borohydride reagent. These aqueous washes can be carried out in either order, and of course, more than one wash with an aqueous inorganic base and/or more than one wash with an aqueous water-soluble borohydride can be utilized.
In washing operation (iii), the inorganic base and the borohydride are combined in the same aqueous solution and utilized in the washing procedure. This simplifies the overall operation and involves less time in conducting the operation. Accordingly, washing operation (iii) is preferred. It will be appreciated that, if necessary or desired, more than one wash with the aqueous alkaline solution of borohydride and inorganic base can be used. Also if necessary or desired, one or more washes with either an aqueous inorganic base or an aqueous solution of a water-soluble borohydride can be utilized before and/or after carrying out one wash, or two or more consecutive washes, with the aqueous alkaline solution of borohydride and inorganic base.
Another embodiment is a process for producing an alkanediol with reduced or eliminated undesirable odor or odor-causing impurities, which process comprises:
a) conducting at least one of the following washing operations on at least one epoxyalkane:
(i) washing the epoxyalkane(s) at least once with an aqueous washing solution of inorganic base, and then washing the epoxyalkane(s) at least once with an aqueous washing solution of borohydride; or
(ii) washing t he epoxyalkane(s) at least once with an aqueous washing solution of borohydride, an d then washing the epoxyalkane(s) at least once with an aqueous washing solution of inorganic base; or
(iii) washing the epoxyalkane(s) at least once with an aqueous washing solution of both inorganic base and borohydride; and
separating the epoxyalkane(s) from the aqueous washing solution or solutions used; and
b) hydrolyzing in the presence of acid or bas e at least one epoxyalkane from a) to form at least one alkanediol.
Still another embodiment is a process of producing an alkanediol, which process comprises:
A) epoxidizing in a liquid phase, an epoxidizable olefinic compound with hydrogen peroxide in the presence of a catalytic quantity of a tungsten-containing catalyst, to form an epoxide;
B) conducting at least one of the following washing operations on said epoxide:
(i) washing said epoxide at least once with an aqueous washing solution of inorganic base, and then washing said epoxide at least once with an aqueous washing solution of borohydride; or
(ii) washing said epoxide at least once with an aqueous washing solution of borohydride, and then washing said epoxide at least once with an aqueous washing solution of inorganic base; or
(iii) washing said epoxide at least once with an aqueous washing solution of both inorganic base and borohydride; and
separating the epoxide from the aqueous washing solution or solutions used; and
C) hydrolyzing in the presence of acid or base th e epoxide from B) to form alkanediol.
These and other embodiments, features, and advantages of this invention will become still further apparent from the ensuing description, accompanying drawings, and appended claims.